Field of the Invention
The present invention relates to an electroconductive member for electrophotography, a process cartridge, and an electrophotographic apparatus.
Description of the Related Art
In an electrophotographic apparatus as an image-forming apparatus adopting an electrophotographic system, an electroconductive member has been finding use in various applications, e.g., an electroconductive roller such as a charging roller, a developing roller, or a transfer roller. The electrical resistance value of such electroconductive roller needs to be controlled to from 103 to 1010Ω independent of its use conditions and use environment. Accordingly, the roller is provided with an electroconductive layer having added thereto an electron conductive agent typified by carbon black or an ion conductive agent such as a quaternary ammonium salt compound, the electron conductive agent or the ion conductive agent being added for adjusting the electroconductivity of the electroconductive layer. Each of those two kinds of electroconductive agents has advantages and disadvantages.
An electron conductive roller obtained by adding the carbon black has the following advantages. A change in its electrical resistance value due to its use environment is small and there is a low possibility that the roller contaminates an electrophotographic photosensitive member (hereinafter referred to as “photosensitive member”). On the other hand, however, the following has been known. It is difficult to uniformly disperse the carbon black, and hence unevenness in the electrical resistance value resulting from the agglomeration of the carbon black occurs, and in particular, there is a possibility that a low-resistance site locally occurs. Even when the addition amount, of the carbon black is adjusted to optimize the electrical resistance value of the entirety of the conductive roller, it is not easy to prevent the local occurrence of the low-resistance site.
In an ion conductive roller obtained by adding the ion conductive agent, the ion conductive agent is uniformly dispersed in a binder resin as compared with the electron conductive roller. Accordingly, unevenness in its electrical resistance value resulting from the dispersion unevenness of the conductive agent can be reduced, and the local occurrence of a low-resistance site observed in an electron conductive system is hardly observed. On the other hand, however, the ion-conducting performance of the ion conductive roller is affected by the amount of moisture in the binder resin under its use environment in an extremely strong manner. Accordingly, it has been known that the electrical resistance value increases owing to the drying of a material for the roller particularly under a low-temperature and low-humidity environment having a temperature of 15° C. and a relative humidity of 10% (hereinafter sometimes referred to as “L/L environment”). Accordingly, it is not easy to secure sufficient electroconductivity under the low-temperature and low-humidity environment.
Japanese Patent Application Laid-Open No. 2000-274424 discloses an approach involving using the ion conductive agent and the electron conductive agent in combination as means for adjusting the electrical resistance value of the electroconductive roller to a proper region independent of its use conditions and use environment.
In addition, Japanese Patent Application Laid-Open No. H08-272187 discloses, as an approach involving uniformizing the electrical resistance of a charging member to uniformly charge the surface of a photosensitive member, a charging member having an electron conductive fiber-entangled body. In addition, Japanese Patent Application Laid-Open. No. H10-186805 discloses, as means for uniformly charging the surface of a body to be charged, a charging device in which a uniform fine void is formed between a charging electrode and the body to be charged by winding a thread-like member around the charging electrode and fixing the member.